In a capacitive or pressure sensor based touch screen, the recognition of a touch or rubbing is easily performed, but, in an acoustic based touch screen which is recently studied, the accuracy of the touch or rubbing recognition is limited.
Although a more complicated design such as the surface roughness, the pad structure, etc. is required, it is difficult to implement the AUI. For example, while the surface roughness of the AUI apparatus needs to vary so as to distinguish the sound wave depending on the direction of rubbing when rubbing, it is very difficult to implement the surface roughness at which generated sound waves are different, since the difference of the sound waves is very small. Also, in a case where the sense of touch is recognized to be dependent on the change of the surface illumination intensity, etc. by a touch or rubbing, it still has structural limitations in recognizing the direction of a touch or rubbing based on sound wave.